Interplay of phytohormones and epigenetic regulation: A recipe for plant development and plasticity

Both phytohormone signaling and epigenetic mechanisms have long been known to play crucial roles in plant development and plasticity in response to ambient stimuli.Indeed,diverse signaling pathways mediated by phytohormones and epigenetic processes integrate multiple upstream signals to regulate various plant traits.Emerging evidence indicates that phytohormones and epigenetic processes interact at multiple levels.In this review,we summarize the current knowledge of the interplay between phytoho...     

Sugar and phytohormone response pathways: navigating a signalling network

Many plant developmental, physiological and metabolic processes are regulated, at least in part, by nutrient availability. In particular, alterations in the availability of soluble sugars, such as glucose and sucrose, help regulate a diverse array of processes. Multiple lines of evidence indicate that many of these processes are also regulated in response to other signalling molecules, such as phytohormones. This review draws examples from a variety of plant systems, including bean, Arabidopsis, potato, and cereals. Five of the most interesting and best developed examples of processes regulated via 'interactions' or 'crosstalk' between sugars and phytohormones are described, including embryogenesis, seed germination, early seedling development, tuberization, and the regulation of alpha-amylase activity. The types of mechanisms by which different response pathways are known or postulated to interact are also described. These mechanisms include regulation of the metabolism and/or transport of a signalling molecule by a different response pathway. For example, sugars have been postulated to help regulate the synthesis, conjugation and/or transport of phytohormones, such as gibberellins and abscisic acid. Conversely, phytohormones, such as abscisic acid, gibberellins and cytokinins have been shown to help regulate sugar metabolism and/or transport. Similarly, sugars have been shown to regulate the expression of components of phytohormone-response pathways and phytohormones regulate the expression of some genes encoding possible components of sugar-response pathways. Examples of proteins and second messengers that appear to act in multiple response pathways are also described.     

油菜素甾醇类与生长素的相互作用

油菜素甾醇类(brassinosteroid,BR)和生长素是两类重要的植物激素,二者在许多生理功能上存在相关性。近年来的研究表明,BR与生长素能协同调节基因表达,二者在代谢、运输和信号转导途径等不同层次上存在相互作用,并且这两种信号与其他信号转导途径,如激素信号转导途径和光信号转导途径之间也存在信号对话。现对BR与生长素之间这种复杂的相互作用进行评述。     

Plant hormones and plant growth regulators in plant tissue culture

Summary This is a short review of the classical and new, natural and synthetic plant hormones and growth regulators (phytohormones) and highlights some of their uses in plant tissue culture. Plant hormones rarely act alone, and for most processes— at least those that are observed at the organ level—many of these regulators have interacted in order to produce the final effect. The following substances are discussed: (a) Classical plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene and growth regulatory substances with similar biological effects. New, naturally occurring substances in these categories are still being discovered. At the same time, novel structurally related compounds are constantly being synthesized. There are also many new but chemically unrelated compounds with similar hormone-like activity being produced. A better knowledge of the uptake, transport, metabolism, and mode of action of phytohormones and the appearance of chemicals that inhibit synthesis, transport, and action of the native plant hormones has increased our knowledge of the role of these hormones in growth and development. (b) More recently discovered natural growth substances that have phytohormonal-like regulatory roles (polyamines, oligosaccharins, salicylates, jasmonates, sterols, brassinosteroids, dehydrodiconiferyl alcohol glucosides, turgorins, systemin, unrelated natural stimulators and inhibitors), as well as myoinositol. Many of these growth active substances have not yet been examined in relation to growth and organized developmentin vitro.     

Jasmonates,New Regulators of Plant Growth and Development: Many Facts and Few Hypotheses on their Actions

Jasmonates, ubiquitous cyclopentanone compounds, are reviewed as new regulators for plant growth and development. They may complement the group of well-established “classic” phytohormones. Jasmonates influence a multiplicity of plant physiological processes by inhibition, promotion or induction. In many aspects they are similar to abscisic acid, especially in responses to stress. The review contains information on the chemical structures and metabolism of jasmonates, contributes to their biological role and describes possible mode(s) of action at the level of molecular biology and gene expression. In particular, emphasis is placed on the gene expression and accumulation of jasmonate-induced abundant polypeptides as a stress response of the plant cells. A hypothesis is attempted in which endogenous jasmonates represent an integral part of the signal transduction chain between stress signal(s) and stress response(s).     

Conjugates of auxin and cytokinin

Plant growth and developmental processes as well as environmental responses require the action and cross talk of phytohormones including auxins and cytokinins. Active phytohormones are changed into multiple forms by acylation, esterification or glycosylation, for example. It seems that conjugated compounds could serve as pool of inactive phytohormones that can be converted to active forms by de-conjugation reactions. The concept of reversible conjugation of auxins and cytokinins suggests that under changeable environmental, developmental or physiological conditions these compounds can be a source of free hormones. Phytohormones metabolism may result in a loss of activity and decrease the size of the bioactive pool. All metabolic steps are in principle irreversible, except for some processes such as the formation of ester, glucoside and amide conjugates, where the free compound can be liberated by enzymatic hydrolysis. The role, chemistry, synthesis and hydrolysis of conjugated forms of two classes of plant hormones are discussed.     

植物激素在苔藓生长发育与逆境响应过程中的作用机制研究进展

植物激素是由植物自身代谢产生的一类从产生部位移动到作用部位发挥调控功能的微量小分子有机物质,在植物生长发育、响应环境胁迫过程中起到关键作用.苔藓植物作为早期登陆的非维管植物,处于陆生植物进化早期的阶段,具有许多不同于维管植物的形态和生理特征.大部分苔藓中普遍存在8种主要的植物激素及其衍生物(包括ABA、JA、ET、SA...     

Effect of Cyclanilide on Auxin Activity

Cyclanilide is a plant growth regulator that is registered for use in cotton at different stages of growth, to either suppress vegetative growth (in combination with mepiquat chloride) or accelerate senescence (enhance defoliation and boll opening, used in combination with ethephon). This research was conducted to study the mechanism of action of cyclanilide: its potential interaction with auxin (IAA) transport and signaling in plants. The activity of cyclanilide was compared with the activity of the auxin transport inhibitors NPA and TIBA. Movement of [³H]IAA was inhibited in etiolated corn coleoptiles by 10 μM cyclanilide, NPA, and TIBA, which demonstrated that cyclanilide affected polar auxin transport. Although NPA inhibited [³H]IAA efflux from cells in etiolated zucchini hypocotyls, cyclanilide had no effect. NPA did not inhibit the influx of IAA into cells in etiolated zucchini hypocotyls, whereas cyclanilide inhibited uptake 25 and 31% at 10 and 100 μM, respectively. Also, NPA inhibited the gravitropic response in tomato roots (85% at 1 μM) more than cyclanilide (30% at 1 μM). Although NPA inhibited tomato root growth (30% at 1 μM), cyclanilide stimulated root growth (165% of control at 5 μM). To further characterize cyclanilide action, plasma membrane fractions from etiolated zucchini hypocotyls were obtained and the binding of NPA, IAA, and cyclanilide studied. Cyclanilide inhibited the binding of [³H]NPA and [³H]IAA with an IC₅₀ of 50 μM for both. NPA did not affect the binding of IAA, nor did IAA affect the binding of NPA. Kinetic analysis indicated that cyclanilide is a noncompetitive inhibitor of both NPA and IAA binding, with inhibition constants (K _i) of 40 and 2.3 μM, respectively. These data demonstrated that cyclanilide interacts with auxin-regulated processes via a mechanism that is distinct from other auxin transport inhibitors. This research identifies a possible mechanism of action for cyclanilide when used as a plant growth regulator.     

水稻根分泌激素调节生长速度

植物激素是植物体内合成的一类重要小分子物质,其含量可因外界条件变化而改变,并作为信号物质调控植物生长发育和适应环境。水培所用介质体积过小会造成植物生长受限、植株矮小,通常认为是小体积生长介质中营养成分不足所致。研究表明,在不同体积且不含任何营养物质的纯水中培养的水稻(Oryza sativa)亦表现出不同的生长速度,幼...     

Growth Based Morphogenesis of Vertebrate Limb Bud

Many genes and their regulatory relationships are involved in developmental phenomena. However, by chemical information alone, we cannot fully understand changing organ morphologies through tissue growth because deformation and growth of the organ are essentially mechanical processes. Here, we develop a mathematical model to describe the change of organ morphologies through cell proliferation. Our basic idea is that the proper specification of localized volume source (e.g., cell proliferation) is able to guide organ morphogenesis, and that the specification is given by chemical gradients. We call this idea “growth-based morphogenesis.” We find that this morphogenetic mechanism works if the tissue is elastic for small deformation and plastic for large deformation. To illustrate our concept, we study the development of vertebrate limb buds, in which a limb bud protrudes from a flat lateral plate and extends distally in a self-organized manner. We show how the proportion of limb bud shape depends on different parameters and also show the conditions needed for normal morphogenesis, which can explain abnormal morphology of some mutants. We believe that the ideas shown in the present paper are useful for the morphogenesis of other organs.     

The Roles of Phytohormones in Development as Studied in Transgenic Plants

The study of transgenic plants has greatly advanced our understanding of the control of development and metabolism. The ability to isolate and modify genes greatly extends the range of what is technically feasible. In the area of hormone biology, transgenic plants have helped to elucidate the pathways of synthesis, the metabolic control points, and the biological functions of the various phytohormones. This review covers the available genes that modulate the metabolism and perception of the phytohormones. One of the most significant conclusions coming out of transgenic plant work is the complex interaction among the different classes of phytohormones. For example, increasing the level of the auxin indole-3-acetic acid (IAA) in a plant has the secondary effect of inducing ethylene biosynthesis. This complication can be circumvented by combining transgenic plants modulating multiple hormones or through the use of available mutants. In this manner, transgenic plants have been utilized to unambiguously define the roles of auxin, cytokinin, and ethylene in the control of apical dominance. The power of transgenic plants as tools in hormone biology is perhaps best illustrated by work on ethylene. In this case, the modular characterization of genes led to elucidation of the biosynthetic pathway. Availability of the biosynthetic genes has permitted detailed analysis of the regulation of synthesis, definition of the role of ethylene in the control of several developmental processes, and the application of that knowledge for agricultural improvement.     

Changes in radical scavenging activity of normal,endoreduplicated and depolyploid root tip cells of Allium cepa

The plant cell responds to abiotic stress conditions by adjusting its cellular metabolism and various defensive mechanisms. Cellular metabolism involves changes in the cell cycle, in which the cell undergoes repeated rounds of endocycles leading to polyploidization. Defense mechanisms such as role of antioxidants are a key to understand plant adaptation. The present work describes endoreduplication and radical scavenging activity as two different defense mechanisms adapted by plants for their survival under stress condition. The work describes linkage of these two processes with each other under abiotic stress. Endoreduplicated root tip cells of Allium cepa were depolyploidized by exogenous phytohormones. Further, free radical scavenging activity from normal, endoreduplicated and depolyploidized root tips cells was observed to understand the role of phytohormones. Elevated free radical scavenging potential was observed in endoreduplicated cells compared to normal and depolyploidized cells. Based on these results, it was concluded that endoreduplication and antioxidant pathways are linked with each other through phytohormonal activities. The concentration of auxin and cytokinin regulates the activity of ascorbate oxidase enzyme, which in turn maintains the concentration of AsA within the cell. AsA level directs the prolyl-hydroxylation process of cell division proteins in quiescent center cells either toward endoreduplication process or cell division process.     

Phytohormones in algae

In various algal taxa, essentially all known phytohormones were detected in concentrations comparable with their content in higher plants. The occurrence of diverse free and conjugated hormone forms substantiates the functioning of the complex system of metabolism and activity regulation of these compounds. In most cases, the spectrum of biological activities of algal hormones corresponds to the functions of higher plant hormones. Some physiological and biochemical processes in algal cells and tissues are under the control of several phytohormones. All these facts permit a consideration of the algal hormonal system as a full-value regulatory system.     

Biophysics of nerve excitation

Experimental studies testifying to the presence of an interrelation between the physiological functions of the organism and physical and chemical processes in nerves are discussed. Changes in some physical and chemical parameters observed both upon elicited rhythmic excitation of nerves and during the spontaneous rhythmic activity of neurons are analyzed. Upon rhythmic excitation, a complex of physical and chemical processes is triggered, and reversible structural and metabolic rearrangements at the subcellular and molecular levels occur that do not take place during the generation of a single action potential. Thus, only in conditions of rhythmic excitation of a nerve, it is possible to reveal those processes that provide excitation of nerves in the organism. The future possibilities of the investigations combining the biophysical and physiological approaches are substantiated. Characteristic changes in physicochemical parameters are observed in nerves during the generation of a series of action potentials of different frequency and duration (“frequency dependence”) under normal physiological conditions, as well as in extreme situations and in nerve pathology. The structural and metabolic rearrangements are directly related to the mode of rhythmic excitation and proceed both in the course of rhythmic excitation and after its termination. Shown also is participation of the basic components of the nervous trunk (axon, Schwann cell, myelin, subcellular organelles) in the realization of rhythmic excitation. In the coordination of all processes involved in rhythmic excitation, the main role is played by the systems of redistribution and transport of intercellular and intracellular calcium. The idea is put forward that myelin of nerve fibers is not only an insulator, but also an “intercellular depot” of calcium and participates in the redistribution of different ions. Thus, the rhythmic excitation is of great importance in the realization of some physiological functions, the adaptation to changing conditions, the liquidation of consequences of paralogical processes, the formation of mechanisms of “memory,” etc.     

植物的环境信号分子茉莉酸及其生物学功能

茉莉酸信号分子参与植物生长发育众多生理过程的调控,尤其是作为环境信号分子能有效地介导植物对生物及非生物胁迫的防御反应。迄今已知具有信号分子生理功能的至少包括茉莉酸(jasmonic acid,JA)以及茉莉酸甲酯(methyl jasmonate,Me JA)和茉莉酸-异亮氨酸复合物(jasmonoyl-isoleucine,JA-Ile)等茉莉酸衍生物,统称为茉莉酸类化合物(jasmonates,JAs)。从环境信号分子角度介绍了茉莉酸信号的启动(环境信号感知与转导、茉莉酸类化合物合成)、传递(局部传递、维管束传输、空气传播)和生物学功能(茉莉酸信号受体、调控的转录因子、参与的生物学过程)。